AFB Motorcycles

Mikuni's Research and Development Department has spent many months to improve the HS carburetor series to meet all the street riders performance needs. First step was a larger body to fill the need for bigger throttle bores in all-out performance applications; step two had to be a smoother and easier throttle operation. This resulted in the design of the HSR42 carburetor. A major feature of the HSR42 is the flat throttle slide assembly with roller bearings. Unlike butterfly throttle valves, which obstruct the carburetor's venturi at all throttle openings, creating airflow turbulence and hindering precise air/fuel metering, the flat throttle slide allows an unobstructed venturi at full throttle, thus flowing more air and carbureting more precisely at all throttle settings. The roller bearings on throttle slide provide a light throttle action, which offers smoother control and allows the use of a very light throttle-return spring. With its 42mm venturi, the HSR42 flows 20% more air than the HS40, making the HSR42 an ideal carburetor for Evolution Big Twin and Twin Cam engines employing other performance modifications such as big bore kits, cams, pistons and an exhaust system (Mikuni still recommends the smaller HS40 carburetor for stock and mild tuned Evolution Sportsters). Flow bench tests by Jerry Branch show that the HSR42 Mikuni, while still being smaller in venturi size to some other popular carburetors, is able to flow more air to the engine once installed on the manifold and head. The HSR42 Mikuni actually flows more air at full throttle to produce more peak power. At partial throttle openings, the Mikuni's smaller, yet higher velocity flowing venturi, together with its advanced fuel-metering system provides a stronger overall powerband with improved ridability. Other performance features of the HSR42 include a larger capacity float bowl and a higher flowing needle-valve assembly to accommodate extended full throttle operation. Also, more positive action of the high leverage float valve prevents the possibility of the float bowl over filling or the needle-valve flooding. This eliminates the need for overflow and vent tubes on the carburetor body, giving the carburetor a cleaner look. An adjustable accelerator pump provides instant throttle response throughout the RPM range. Kits work with 1990 thru 2017 style Big Twin throttle and idle cables. Other features are instant engine response, improved rider throttle control, more mid range power for faster acceleration and passing with more confidence, good gas mileage and years of dependable service. Installation instructions and hardware are included with each kit. Mikuni developed several kits for special applications as well as "Easy Kits" that use stock manifolds, choke cable, air cleaner and throttle cable.

Throttle and idle cables for use with Mikuni HSR42, and HSR45 carburetors Early style HSR42 and HSR45 carburetors have the cable wheel on the left side of the carburetor and use cables as in the table above. Late style HSR42 and HSR45 carburetors have the cable wheel on the right side of the carburetor and use 1990 or later OEM style cables as used on Big-Twin models. Most cables are available in black vinyl or braided steel.

Instructions

Specifications

Total Kit, fits Evolution Big Twin models 1984-1999, except 1984 thru 1988 FLH and FLT.
All 1984-1989 models require the seperate purchase of mounting flanges ZPN 234039 & 234040 and seals ZPN 740343
Includes performance intake manifold, rubber mounting flange, HSR42 carburetor, high flow K&N filter, Chrome air cleaner cover, breather kit and hardware. Uses stock style 1990-2017 Big Twin throttle and idle cables.
Article number Description Retail price Add to list
Total Kit
Total Kit, TÜV approved
Total Kit, fits Twin Cam models 1999 thru 2017
Includes performance intake manifold, rubber mounting flange, HSR42 carburetor, high flow K&N filter, Chrome air cleaner cover, breather kit and hardware. Uses stock throttle and idle cables.
Article number Description Retail price Add to list
Total Kit for Twin Cam
Easy Kit, uses stock manifolds, choke cable, air cleaner and throttle cable

Easy Kit for 1200 Sportster models 1994 to present

Includes HSR42 carburetor, special backing plate and hardware. Use the stock oval cover and a high flow replacement filter.

Note:
Use in combination with same year stock style Big Twin throttle cables. These must be ordered separately
Article number Description Retail price Add to list
Easy Kit for 1200 Sportster
Easy Kit for Evolution Big Twin models 1990 thru 1999
Includes HSR42 carburetor, air cleaner adapter and chrome cover. Uses stock style cables.
Note:
Does not work with cruise control.
Article number Description Retail price Add to list
Easy Kit for Evolution Big Twin
Easy Kit for Evolution Big Twin, TÜV approved
Easy Kit for Twin Cam models
Includes HSR42 carburetor, air cleaner adapter for Screamin' Eagle filter, and instructions. Use with stock style throttle cables and air cleaner cover. Will not work with stock air box or cruise control.
Article number Description Retail price Add to list
Easy Kit for Twin Cam
Economy Kit
Includes 42mm HRS carburetor and air cleaner adaptor to install a 1990 to present style air cleaner. Uses 1990 thru 1995 stock style cables.
Article number Description Retail price Add to list
Economy Kit
Economy Kit, TÜV approved for Evolution Big Twin FXR, Dyna and Softail models
Mikuni HSR42 carburetor only
Pull (throttle) cables
Article number Description Retail price Add to list
Black cable, stock length thru 1995
Black cable, +4" thru 1995
Black cable, +6" thru 1995
Black cable, stock length 1996 to present
Braided steel, clear coated, stock length, thru 1995
Braided cable, +6" thru 1995
Braided steel, clear coated, stock length, 1996 to present
Clear Coated, +6" 1996 to present
Black cable, Buell 1997 to present
Push (idle) cables
Article number Description Retail price Add to list
Black cable, stock length thru 1995
Black cable, +4" thru 1995
Black cable, +6" thru 1995
Black cable, stock length 1996 to present
Braided steel, clear coated, stock length, thru 1995
Braided steel, clear coated, stock length, 1996 to present
Clear coated cable, +6" 1996 to present
Black vinyl, Buell 1997 to present
Replacement parts
Article number Description Retail price Add to list
Air filter element
Chrome air cleaner cover
Chrome air cleaner cover with cutouts
Rubber carburetor-to-manifold mounting flange for early style manifold with round opening
Rubber carburetor-to-manifold mounting flange for late style manifold with oval opening
Manifold for Evolution models
Manifold for Twin Cam models
Complete 8" long choke cable with knob, fits Mikuni HSR42, HSR45 & HSR48 carburetors, can also be used on Keihin CV carburetors
Rebuild kit, includes needle valve assembly, top cover gasket, spigot body seal, float bowl seal, rubber boot for accelerator rod, and O-rings
Fuel screw washer
Fuel screw O-ring

Recommended Retail Prices include 20% sales tax.

Prices exclude shipping, import duties and installation.

Prices are based on EUR to GBP interbank rates obtained daily. The interbank rate is the rate that banks trade currency to each other. These prices must be used as a guide.